The Abyss

The Abyss is a vast wound in the cosmic order, a bottomless pit teeming with creatures that exist only to rend, tear, and destroy. The demon princes, individual demons of great power and determination, bend and shape the Abyss and its inhabitants to meet their every whim. These mighty beings imagine themselves at the center of the cosmos. Each demon prince believes that the universe will one day be theirs to command, its laws and structure twisted and warped to match the demons’ ideal of perfection.
The demon princes’ arrogance is exceeded only by their ambition. While any rational being would dismiss their goals as empty ambitions sparked by madness, the truth remains that the demon princes and their thralls are among the mightiest forces in the planes. It is conceivable that, if the Blood War turns dramatically in their favor, the demon princes could put the rest of their apocalyptic plans in motion.
Although sages group demons into types according to their power, the Abyss knows no such categories. Demons are spawned from the stuff of the Abyss in a near-infinite variety of shapes and abilities. The common forms that are familiar to demonologists represent broad trends, but individual demons defy those tendencies. For instance, a vrock might crawl out of an oil slick in the Demonweb Pits with three eyes and vestigial wings. A chasme might appear on the layer of Azzagrat possessing the ability to belch forth clouds of flies.
If a demon survives for centuries, it accumulates changes to its form due to interaction with the energies of the Abyss. These long-lived demons often become demon lords, beings of such power that they can hold sway over entire realms within the Abyss. A few demon lords have come to the attention of mortals and are even worshiped as gods in some places, but the vast majority of demon lords remain unknown to scholars and sages.

The Unknowable Abyss

The Abyss is a puzzle to those who study demons and an attraction for those who seek power. It isn’t as purely chaotic as Limbo nor as pliable, and yet demon lords can shape its essence by their subconscious will. Some demon lords emerge from the planar stuff, others seem to have been in existence since the start of time, and still others are interlopers from outside the Abyss. Several theories exist about what principles dictate who can gain a demon lord’s power, or, if no such principles exist, how that power might be seized.
Most mortals would rather be annihilated than have their souls travel to the Abyss, but some see its chaos as something that can be harnessed and manipulated by those of sufficient will. A powerful soul might be able to dominate demons, retrieve weapons of the Blood War to use in mortal conflicts, or discover spells known only in the Abyss — and the madly ambitious might even seek out the means of becoming a demon lord.

Ever-Changing Layers

The physical nature of the Abyss is something that few mortal minds can understand. Those who discuss such matters use the term “layer” to define a certain part of this infinite expanse. That nomenclature, to the extent that it implies a particular configuration, is misleading.
The Abyss is a chaotic tangle of miniature worlds, each one shaped by the demon lord that claims primacy over it. Within the layers it controls, a demon lord manipulates conditions to match its view of how that world best serves the lord’s desires.
Of course, keeping control of a layer involves fighting off other demons that are looking to expand their domains. From time to time, a layer changes hands or is seemingly obliterated in a battle (perhaps to be reborn in another location). For this reason, imposing a sense of order on the relationship between the Abyss’s layers is a fool’s errand. All that can be determined at any given time is which lord holds sway over which parts of the Abyss, and which areas are being contested by two or more lords. And as soon as such a fact becomes known, it might already be obsolete.

Getting Around

Portals connect various locations in the Abyss, but these passages are as unreliable as anything else in this environment. Most of them fluctuate, sometimes winking in and out of existence or connecting to different layers at random. Rituals exist that travelers can use to attune a portal to a certain domain. However, the exact specifications of such a ritual vary for each potential destination.
Those who would navigate the Abyss always enter the place in a random location. From there, they must locate a portal and then perform the ritual that enables them to find a specific destination. Escaping the Abyss likewise requires knowledge of the specific ritual needed to do so. Without it, visitors are trapped unless they have access to magic that permits travel between planes.

Demonic Incursions

The Abyss and its demonic inhabitants are akin to a virus. While most other factions across the planes spread their influence into other realms through conquest, conversion, or diplomacy, demons infect a world by traveling there and beginning to transform their environment to resemble the malleable, chaotic substance of their home plane. If demons dwell in a place for a significant amount of time, the area starts to warp in response to the abyssal energy that churns within it. If a demonic infestation is left unchecked, a portal to the Abyss is the result, and more and more of the essence of the Abyss pushes its way through. In time, a plane or a world could become a colony of the Abyss, overrun with demons and devoid of all other forms of life.

Initial Infection

A full-fledged demonic incursion takes time to develop. A demon prince might rampage across a world for a few days or weeks before returning home, but that event doesn’t qualify as an incursion. After the demon is banished, the world suffers no long-term effects, aside from the destruction wrought by the demon.
But if demons can dwell undisturbed on a plane for a period of time, their continued presence begins to erode the barriers between their location and the Abyss. It can take a few years for weaker demons to warp their environment, while changes begin to occur around the location of a demon prince in about a month.
To bring about these changes, the invaders must remain in the same location for some time, usually an area no more than six miles on a side, to combine their influence. Fortunately for their would-be victims, the chaotic evil nature of demons means that they rarely organize in a way to cause such a disturbance. Demons that enter the world are bent on destruction, not concerned with greater matters, and inclined to go their separate ways unless a powerful leader can keep them under control long enough for the virus to take hold.
During the first stages of an abyssal incursion, the natural world recoils from the demonic presence. Plants become twisted versions of themselves. Leering faces appear in leaf patterns, vines writhe of their own accord, and trees grow foul-smelling tumors instead of leaves as their branches wither and die. Bodies of water in the area become tainted and sometimes poisonous, and the weather might feature extremes of heat, cold, wind, rain, or snow that aren’t typical of the normal climate. Living things in the area flee or are killed by the demons.
At this stage, natives can stop the incursion by killing or driving away the demons that infest the area. The effects of the event might persist for a few months or even centuries, but the barriers between the Abyss and the world remain intact.

A Growing Menace

If the first stage of the infection continues long enough, a portal opens in the corrupted environment that connects to a random location in the Abyss. Demons that happen to be near the portal can travel through it and into the world, while the raw stuff of the Abyss also begins to seep through the passage.
Even at this stage, the infection has almost no chance of developing into a true incursion. The immensity of the Abyss means that a portal’s random location is more likely to be an empty, uninhabited place than anything else, and demons can’t make use of the portal unless they can locate it. The incursion might be long delayed as a result, but the portal’s opening on the other plane remains a lurking threat until it is closed.
As more demons find and use the portal, the Abyss becomes strongly linked to the world, and the region’s transformation grows more extreme. The odd but still mundane weather gives way to storms that drop burning embers, or winds that shriek in all directions, seizing living creatures and hurling them against the ground. The environment becomes inimical to all living things.
At this point, the incursion is still in a state of flux. The demons aren’t yet directed by a single will. Unless a powerful demon dominates all the others, the area is wracked by fighting as one demon after another claims primacy, only to be overcome. The tie to the Abyss is still fragile enough that, as demons are slain, the portal grows smaller and weaker. If the invaders are reduced to about half the number that were present when the portal was created, the opening winks out of existence.

A Stain on Reality

In its third phase, the demonic virus invades fully and becomes a part of the world. Simply killing the demons in an afflicted area is no longer enough to remove the Abyss’s stain.
The size of the region begins to grow, the effects of the lethal environment expanding from the original area. The demons likewise begin to roam, and a small force capable of establishing its own incursion might travel far. If enough of these groups splinter off, the incursion could spread into a network of similar sites, each opening its own portal and drawing in more demons.
Slaying all the demons in an infested area ends their direct threat, but the terrain remains twisted and accursed, the portal dormant but still in place. To repel the incursion at this stage, the defenders must not only slay the demons but also establish a permanent watch over the portal, to ensure that it remains unused. Ambitious cultists, or even a random confluence of planar energy, could awaken the portal and start the infection anew.

Apocalypse Now

If the incursion remains unchecked or grows strong enough, it enters its fourth and final phase with the entrance of a demon lord. As a portal continues to shunt demons and abyssal energy into the world, it begins to attract the attention of the lords. Two or more of them might fight for control of it, or in the worst case, several might travel through the portal in rapid succession.
The visitation of a demon lord to the Material Plane is a cataclysmic event. The lord’s presence overwhelms the minds of other beings to keep them from resisting, and the lord’s power enables it to command the other demons already present in the world. They form a horrid army that sets about stripping the world of life and clearing the path for the lord’s dominance.
At this point, a besieged world’s only hope for survival is the expulsion of the demon lord. The lord’s defeat leaves the other demons again leaderless, and they react by warring against each other, which makes them susceptible to attacks from the world’s defenders. The longer a demon lord remains in control of all the other fiends, the more the world around it becomes irrevocably changed. When a demonic incursion runs its course, no vestige remains of the world that existed before — in effect, the realm has become another layer of the Abyss.

Some scholars number and name the parts of the Abyss, declaring that this demon lord or that rules a portion of the place. When your house is on fire, does it matter what the flames look like in each room? Should you bother to give them names? What’s important is escaping and putting out any fire that clings to you.

Included Organizations

• Princes of the Abyss

Owning Organization

Princes of the Abyss

Characters in Location

• Baphomet
• Demogorgon
• Fraz-Urb’luu
• Graz’zt
• Juiblex
• Orcus
• Yeenoghu
• Zuggtmoy